This invention relates to a light sensitive, color photographic silver halide compositions which contain new DIR couplers in order to improve their color rendition and detail rendition.
It is known that one may add to light sensitive silver halide color photographic materials color couplers for the improvement of the quality of the image, which free development inhibitors during the color development proportional to the exposure. They are usually called DIR-couplers ("DIR" meaning "development inhibitor releasing") and are described in detail as to their structure, mechanism of coupling and photographic effect for instance by C. R. Barr, J. K. Thirtle and P. W. Vittum in Phot. Sci. Engn. 13, 274-79 (1969) and in U.S. Pat. No. 3,148,062. Photographic properties which can be improved with DIR-couplers are edge sharpness, color grain and color rendition.
These effects are based upon the diffusion of the freed inhibitor within that layer which contains the DIR-coupler (intra-image effect) and upon the diffusion into the adjacent layer (inter-image effect). The intra-image effect improves the rendition of detail and the inter-image effect may be used for color correction of undesired color layers of image coloring dyes. These effects based upon inhibiting effect and upon diffusion are described by, among others, W. T. Hanson and C. A. Horton in J. Optical Soc. America 42, 633-669 (1952); A. Thiele in Z. Wiss. Photogr., Photophys., Photochem. 47, 105-118 as well as 246-255 (1952) and in Federal Republic of Germany Offenlegungsschrift No. 2,509,722. Furthermore the DIR-couplers may be used according to U.S. Pat. No. 3,620,747 for control of gradation and, in connection with that, for the increase of the brightness of the coloring dyes and, also according to Federal Republic of Germany Offenlegungsschrift No. 2,533,176 for the reduction of development fog, particularly for work at elevated temperatures. The chemical structure of the known DIR-couplers embraces particularly acylacetanilide-, pyrazolone-(5)-, phenol-, or 1-naphthol-derivatives bonded to a usual diffusion-preventing ballast group and in coupling position to a splittable inhibitor group. Particularly effective DIR-couplers carry heterocyclic mercaptoazols, -azines, arylmercaptans or mercapto-carboxylic acids as splittable groups. The most typical diequivalent substituents are 2-nitro-, or 2-aminophenylthio-, benzthiazole-2-ylthio-, 1-phenyl-tetrazole-5-ylthio-, 5-phenyl-1,3,4-oxadiazole-2-ylthio- or benzoxazole-2-ylthio-groups. Syntheses of a multitude of DIR-couplers carrying the typical inhibitor groups are described in, among other places, U.S. Pat. Nos. 3,148,062, 3,227,551, 3,227,554 and in Federal Republic of Germany Offenlegungsschrift No. 2,247,496. The use of prior art DIR-couplers exhibits, though, certain disadvantages. Usually they cannot be used as the single coloring element because the strong inhibiting action of the splitting group retards the chromogenic development so strongly that even development at high temperature results in low saturated images. That necessitates the mixing in of coloring couplers which result in dyestuffs of the same absorption range at a higher yield. Examples of mixtures with two to seven different color couplers and DIR-compounds are shown in U.S. Pat. No. 3,703,375 or Federal Republic of Germany Offenlegungsschrift No. 2,530,645, and their influence upon improvements of definition, grain and color rendition are tabulated. Mixtures contain usually less than 10% of the above-described DIR-couplers. Mostly only incomplete decoupling of the DIR-coupler occurs due to this low concentration of coupler and also because the admixed color coupler exhibits in most cases a higher coupling speed. That leads to low concentrations of freed development inhibitor, in order to render possible particularly efficient inter-image effects by diffusion into adjacent layers. Therefore, special uses of known DIR-couplers are made, for example, in intermediate layers and auxiliary layers, which solely serve to correct color by the inter-image effect. They are, for example, described in U.S. Application No. 454,524, U.S. Pat. No. 3,006,759 and in Federal Republic of Germany Offenlegungsschrift Nos. 2,421,544 and 2,429,250 and are named also IIC-, ILC- or IIE-couplers. The use of higher concentrations of the known DIR-couplers is furthermore limited by the lowering of the sensitivity and gradation by the so-called "clearing effect." It always occurs when freeing of the inhibitor not proportional to illumination occurs before or during the chromogeneous development or when inappropriate purification methods do not succeed in bringing the residual inhibitor content of the DIR-couplers below 0.5%. Adequate purification is technically difficult and expensive and is sometimes very difficult, if not impossible, to achieve on a commercial scale. As an expedient serve complicated systems of layer construction, as claimed for example in U.S. Pat. Nos. 3,620,745, 3,620,747, Federal Republic of Germany Offenlegungsschrift Nos. 2,322,165, 2,421,544, 2,423,250 and 2,530,645. Here known DIR-couplers are introduced into the insensitive silver halide layers of variously constructed layer units of a color forming element in order to improve image definition and color rendition.
Besides the hereabove described DIR-couplers with thio-ether splittable groups of high inhibitor effect, U.S. Pat. No. 3,617,291 mentions, among others, DIR-couplers which have heterocyclic imino-compounds or precursors thereof which could serve as splittable groups. Typical couplers contain benztriazolyl- or nitrobenzimidazolyl- moieties or derivatives thereof. Compared to the aforementioned DIR-couplers having thioether structure, these compounds show too small DIR-effects and are less capable of color correction effects. It might be also disadvantageous that the known DIR-couplers are mostly hydrophobic compounds and that only rarely the usual inhibitor moieties are bound as splittable groups to hydrophilic compounds. They only can be used for photographic material when dispersed, which means an addition of high- or sometimes low-boiling solvents and emulsifiers, which is more expensive than the use of a simple solution.
It is an object of the invention to make possible by the use of new DIR-couplers the preparation of color photographic silver halide multilayer materials of good definition, grain and color rendition, avoiding the disadvantages of present technical solutions such as, for instance, too low intra- and inter-image effects due to a too small DIR-coupler percentage in mixtures with other couplers or the use of a complicated layer construction for a color photographic multilayer material or high costs of production caused by a complicated purification process for the DIR-couplers which are being used. Another aim of the invention is to lower the costs of the aforementioned silver halide materials by using new DIR-couplers which may be added to the color photographic silver halide layers as aqueous alkaline solutions.